Porous polymeric particles have been prepared and used for many different purposes. For example, porous particles have been described for use in chromatographic columns, ion exchange and adsorption resins, drug delivery devices, cosmetic formulations, papers, and paints. The methods for generating pores in polymeric particles are well known in the field of polymer science. However, each particular porous particle often requires unique methods for their manufacture. Some methods of manufacture produce large particles without any control of the pore size while other manufacturing methods control the pore size without controlling the overall particle size.
Marker material can be included in porous particles so that the particles can be detected for a specific purpose. For example, U.S. Patent Applications 2008/0176157 (Nair et al.) and U.S. Pat. No. 8,252,414 (Putnam et al.) and U.S. Pat. No. 7,754,409 (Nair et al.) describe porous particles and a method for their manufacture, which porous particles are designed to be toner particles for use in electrophotography. Such porous particles typically contain a colorant and can be prepared using a multiple emulsion process in combination with a suspension process (such as “evaporative limited coalescence”, ELC) in a reproducible manner and with a narrow particle size distribution.
U.S. Pat. No. 7,887,984 (Nair et al.) describes the use of various hydrocolloids in making porous particles. Porous particles used for these and other purposes are described also in U.S. Pat. No. 8,110,628 (Nair et al.) and U.S. Patent Applications 2012/0167666 (Nair et al.) and 2012/0171605 (Nair et al.). Such porous particles can contain multiple markers in their pores and are prepared from water-in-oil emulsions comprising pore stabilizing hydrocolloids (such as carboxymethyl cellulose), which are then combined with an external water phase to form water-in-oil-in-water emulsions. Pores containing the various markers are provided after removing the various solvents.
U.S. Pat. No. 8,110,628 (Nair et al.) describes porous particles that can be prepared using multiple water-in-oil emulsions containing desired markers and pore stabilizing hydrocolloids to prevent coalescence of the pore forming water-in-oil droplets.
While such pore stabilizing hydrocolloids can be used to provide porous particles from water-in-oil emulsions, the conditions in these emulsions must be ideal, meaning that the oil phase viscosity and elasticity must be optimal, the polymers incorporated into the oil phase must have hydrophilic groups such as carboxylic acid groups to reduce the interfacial tension between the oil phase and the water phase, and pigments that are desirably present in the oil phase or water phase provide additional interface stabilization.
If these conditions do not exist in the water-in-oil emulsions, there is less certainty that desired porous particles can be prepared. The water-oil interface is not always satisfactorily stabilized so that the formation of one or more types of pores optionally with different markers or incorporated chemicals is not predictable. Small molecule emulsifiers (surfactants) have been used to stabilize water-in-oil emulsions but such emulsifiers are dynamic and tend to migrate to other interfaces unpredictably. For example, they can migrate to the external water-oil interface and interfere with the suspension ELC process used to prepare porous polymeric particles.
There is a need for better materials that can stabilize the water-in-oil emulsions in conjunction with the pore stabilizing hydrocolloids for oil phases that do not have the ideal properties to provide interface stabilization. Therefore, there is a need for a more reliable method for preparing porous particles with such oil phases where there is more predictability in the resulting materials.